Role of the Perfluoro Effect in the Selective Photochemical Isomerization of Hexafluorobenzene. Cox, J. M., Bain, M., Kellogg, M., Bradforth, S. E., & Lopez, S. A. Journal of the American Chemical Society, 143(18):7002–7012, American Chemical Society (ACS), 2021. 
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Paper doi abstract bibtex 2 downloads Hexafluorobenzene and many of its derivatives exhibit a chemoselective photochemical isomerization, resulting in highly strained, Dewar-type bicyclohexenes. While the changes in absorption and emission associated with benzene hexafluorination have been attributed to the so-called “perfluoro effect”, the resulting electronic structure and photochemical reactivity of hexafluorobenzene is still unclear. We now use a combination of ultrafast time-resolved spectroscopy, multiconfigurational computations, and non-adiabatic dynamics simulations to develop a holistic description of the absorption, emission, and photochemical dynamics of the 4π-electrocyclic ring-closing of hexafluorobenzene and the fluorination effect along the reaction coordinate. Our calculations suggest that the electron-withdrawing fluorine substituents induce a vibronic coupling between the lowest-energy 1B2u (ππ*) and 1E1g (πσ*) excited states by selectively stabilizing the σ-type states. The vibronic coupling occurs along vibrational modes of e2u symmetry which distorts the excited-state minimum geometry resulting in the experimentally broad, featureless absorption bands, and a ∼100 nm Stokes shift in fluorescence—in stark contrast to benzene. Finally, the vibronic coupling is shown to simultaneously destabilize the reaction pathway toward hexafluoro-benzvalene and promote molecular vibrations along the 4π ring-closing pathway, resulting in the chemoselectivity for hexafluoro-Dewar-benzene.
@article{Cox_2021,
doi = {10.1021/jacs.1c01506},
url = {https://doi.org/10.1021%2Fjacs.1c01506},
year = 2021,
publisher = {American Chemical Society ({ACS})},
volume = {143},
number = {18},
pages = {7002--7012},
author = {Jordan M. Cox and Matthew Bain and Michael Kellogg and Stephen E. Bradforth and Steven A. Lopez},
title = {Role of the Perfluoro Effect in the Selective Photochemical Isomerization of Hexafluorobenzene},
journal = {Journal of the American Chemical Society},
abstract = {Hexafluorobenzene and many of its derivatives exhibit a chemoselective photochemical isomerization, resulting in highly strained, Dewar-type bicyclohexenes. While the changes in absorption and emission associated with benzene hexafluorination have been attributed to the so-called “perfluoro effect”, the resulting electronic structure and photochemical reactivity of hexafluorobenzene is still unclear. We now use a combination of ultrafast time-resolved spectroscopy, multiconfigurational computations, and non-adiabatic dynamics simulations to develop a holistic description of the absorption, emission, and photochemical dynamics of the 4π-electrocyclic ring-closing of hexafluorobenzene and the fluorination effect along the reaction coordinate. Our calculations suggest that the electron-withdrawing fluorine substituents induce a vibronic coupling between the lowest-energy 1B2u (ππ*) and 1E1g (πσ*) excited states by selectively stabilizing the σ-type states. The vibronic coupling occurs along vibrational modes of e2u symmetry which distorts the excited-state minimum geometry resulting in the experimentally broad, featureless absorption bands, and a ∼100 nm Stokes shift in fluorescence—in stark contrast to benzene. Finally, the vibronic coupling is shown to simultaneously destabilize the reaction pathway toward hexafluoro-benzvalene and promote molecular vibrations along the 4π ring-closing pathway, resulting in the chemoselectivity for hexafluoro-Dewar-benzene.},
bibbase_note = {<img src="https://pubs.acs.org/cms/10.1021/jacs.1c01506/asset/images/medium/ja1c01506_0011.gif">}
}
Downloads: 2
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While the changes in absorption and emission associated with benzene hexafluorination have been attributed to the so-called “perfluoro effect”, the resulting electronic structure and photochemical reactivity of hexafluorobenzene is still unclear. We now use a combination of ultrafast time-resolved spectroscopy, multiconfigurational computations, and non-adiabatic dynamics simulations to develop a holistic description of the absorption, emission, and photochemical dynamics of the 4π-electrocyclic ring-closing of hexafluorobenzene and the fluorination effect along the reaction coordinate. Our calculations suggest that the electron-withdrawing fluorine substituents induce a vibronic coupling between the lowest-energy 1B2u (ππ*) and 1E1g (πσ*) excited states by selectively stabilizing the σ-type states. The vibronic coupling occurs along vibrational modes of e2u symmetry which distorts the excited-state minimum geometry resulting in the experimentally broad, featureless absorption bands, and a ∼100 nm Stokes shift in fluorescence—in stark contrast to benzene. Finally, the vibronic coupling is shown to simultaneously destabilize the reaction pathway toward hexafluoro-benzvalene and promote molecular vibrations along the 4π ring-closing pathway, resulting in the chemoselectivity for hexafluoro-Dewar-benzene.","bibbase_note":"<img src=\"https://pubs.acs.org/cms/10.1021/jacs.1c01506/asset/images/medium/ja1c01506_0011.gif\">","bibtex":"@article{Cox_2021,\n\tdoi = {10.1021/jacs.1c01506},\n\turl = {https://doi.org/10.1021%2Fjacs.1c01506},\n\tyear = 2021,\n\tpublisher = {American Chemical Society ({ACS})},\n\tvolume = {143},\n\tnumber = {18},\n\tpages = {7002--7012},\n\tauthor = {Jordan M. Cox and Matthew Bain and Michael Kellogg and Stephen E. Bradforth and Steven A. 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